By performing an electric discharge machining process, it is possible to process metal into any desired shape without being affected by the level of hardness of the metal. Electric discharge machining processes are also used as a method for cutting a wafer that has a large diameter out of a semiconductor ingot. During an electric discharge machining process to cut out such a wafer, electric discharges are generated in the manner of pulses, with the electric discharge point being shifted, for the purpose of preventing the level of precision of the machining process from being degraded by having the electric discharge positions concentrated in one place. And due to this, the speed of the machining process tends to be low. To cope with this situation, a method for improving the speed of the machining process has been proposed, as disclosed in Patent Document 1, by which a slicing process is performed on a semiconductor ingot while a plurality of wires are arranged in parallel.
According to this method, however, if the plurality of wires were driven by one electric power source, when one of the wires has an electric discharge, the voltages applied to the other wires would become lower, and it would become impossible to cause the other wires to generate electric discharges. For this reason, it is necessary to provide an electric power source for each of the wires individually, and that leads to a state in which the electric discharge machining apparatus has a large size and a high cost.
Further, to realize excellent processing characteristics that make it possible to obtain, for example, a processed surface having high quality, Patent Document 2 discloses a method by which an alternating-current high-frequency wave is applied to an electrode, while an average processing voltage is arranged to be zero so as to prevent chipping, and also, the electric discharge point is arranged to be different for each electric discharge by switching the polarity for every single half-wave electric discharge.
Further, as a method for causing a plurality of wires to generate electric discharges by using one electric power source, Patent Document 3 discloses a method by which a capacitor is provided so as to be connected in parallel to each of a plurality of electric discharge gaps, and these capacitors are configured so as to be electrically charged via diodes.